Infiltration of the central nervous system by neoplastic cells in patients with glioblastoma multiforme (GBM) leads to neurological dysfunction and eventually to death. Gliomas contain specific histologic subtypes, the most common of which are astrocytomas, oligodendrogliomas, and ependymomas. They are a highly invasive, rapidly spreading form of brain cancer that is resistant to surgical and medical treatment. These tumors have been classified as grade I to grade IV on the basis of histopathological and clinical criteria established by the World Health Organization (WHO) (Louis, D. N. et al. (2007) Acta Neuropathol. 114:97). Generally, WHO grade I gliomas, considered to be benign, are often curable with complete surgical resection and rarely, if ever, evolve into higher grade lesions (Burger, P. C. et al. (eds.) (2000) Pathology and Genetics of Tumours of the Nervous System. IARC Press, Lyon pp. 45-51). In contrast, gliomas of WHO grade II or III are invasive, progress to higher-grade lesions, and have a poor outcome. Despite advances in surgical techniques, radiation therapy and adjuvant chemotherapy, WHO grade IV tumors (glioblastomas), which are the most invasive form, have a very poor prognosis (Strupp, R. et al. (2005) N. Engl. J. Med. 352:987; Wen, P. Y. et al. (2008) N. Engl. J. Med. 359:492).
Isocitrate dehydrogenase (IDH) is an enzyme that catalyzes the oxidative decarboxylation of isocitrate (ICT) to produce α-ketoglutarate (αKG). The activity of IDH is dependent on either nicotinamide adenine dinucleotide phosphate (NADP+-dependent IDH1 and IDH2) or nicotinamide adenine dinucleotide (NAD+-dependent IDH3). An unbiased, genome-wide analysis of the somatic mutations occurring in GBMs revealed recurrent mutations in R132, the active site of IDH1, a gene with no known link to gliomas, in 12% of tumors analyzed (see, e.g., Parsons, D. W. et al. (2008) Science 321:1807). Intriguingly, mutations of IDH1 predominantly occurred in younger patients, were associated with a better prognosis, and were preferentially found in tumors that possessed TP53 mutations but lacked other common GBM alterations: all characteristics of secondary GBMs. Additional studies have confirmed that IDH1 is mutated in >80% of secondary GBMs, whereas <10% of primary GBMs harbor these alterations (see, e.g., Balass, J. et al. (2008) Acta. Neuropathol. 597:602; Bleeker, F. E. et al. (2009) Hum. Mutat. 30:7; Yan, H. et al. (2009) N. Engl. J. Med. 360:765; Ichimura, K. et al. (2009) Neurooncol. 11:341; Kang, M. R. et al. (2009) Int. J. Cancer 125:353; Watanabe, T. et al. (2009) Am. J. Pathol. 174:1149). Mutations were recently identified that affected amino acid 132 of IDH1 in more than 70% of WHO grade II and III astrocytomas and oligodendrogliomas and in glioblastomas that developed from these low grade lesions. IDH1 and IDH2 mutations are also present in 23% of acute myeloid leukemia, but are rarely observed in other types of cancers, suggesting that IDH1 mutant dependent on specific cell type or cell environment. By far, the most common mutation seen in glioma patients is IDH1R132H.
In the past, researchers have had to rely on primary cultures of astrocytoma cells for cancer research. Such cultures have been of limited value, however, for the following reasons: (1) human astrocytoma cells are difficult to obtain; (2) very small numbers of cells can be obtained and cultured; and (3) the cultures can be maintained for short periods of time and die quickly. The establishment of an IDH1-mutated human astrocytoma cell line is therefore of significant value as it obviates the need for using primary cultures and enables scientists to perform studies that would not have been possible using primary cultures. Such a cell line would have utility for studies including those aimed at (1) determining the function of the IDH1 gene in human glioma cells; (2) studying gene-gene interactions, in order to elucidate the molecular mechanisms involved in tumorigenesis and molecules that may be drug targets; (3) identifying genes whose expression is altered as a consequence of IDH1 inactivation and this alteration, in order to identify those genes that determine the time of onset and severity of disease in different individuals; (4) making xenografts for in vivo animal models; and (5) screening for therapeutic agents that are effective in killing, or reducing/inhibiting the growth of the cells.